Elimination of interference in carrier systems



June 2, 1925- 1,539,903

L. M. ILGENFRITZ ELIMINATION OF INTERFERENCE IN CARRIER SYsTEMS Filed May 21, 1924 IN VEN TOR A TTORNE Y Patented June 2, 1925.

UNITED STATES PATENT OFFICE.

LESTER MT. ILGENFRITZ, OF ORANGE, NEW JERSEY, ASSIGNOLR TO AMERICAN TELE- PHONE AND TELEGRAPH COIIIPANY, A CORPORATION OF NEW YORK.

ELIMINATION OF INTERFERENCE IN CARRIER SYSTEMS.

Application filed May 21, 1924. Serial No. 714,931.

To all whom it may concern:

Be it known that I, Lnsrna M. ILoENFnrrz, residing at Orange, in the county of Essex and State of New Jersey, have invented certain IIHPI'OVGIDQIltS in Elimination of Interference in Carrier Systems, of which the following is a specification.

This invention relates to carrier systems and more particularly to the elimination of external interference in such systems.

In systems employing carrier frequencies for the transmission of signals, one of the principal sources of external interference is due to radio transn'iitters employing frequencies lying within the range transmitted by a carrier channel. Such interference is produced by the line wires acting as an antenna to pick up the radiated wave and transmit it to the receiving airrier apparat us.

It has lwretofore been, proposed to overcome interference of this sort by picking up a component interfering wave and im- 1iiressing it upon the circuit at some point common to all of the carrier channels, with such phase and amplitude as to neutralize the interferin com )onent transmitted over.

the line wires. Some difficulty has been found in applying this method, however, because of the lacl: of stability of the balance obtained. This lack of stability may arise from changes in the frequencies of the interfering radio transmitters, fromv changes in the propagation constant of the telephone line from temperature, humidity, etc., and changes in the propagation of the electroniagnetio waves radiated from the radio transmitter due to the movements of clouds, etc.

Such changes are not controllable at the receiving carrier terminal and they are suiiicient to displace the condition of balance in a very short period of time. In order to avoid the necessity of having an attendant constantly supervising the system to keep it pro n-a-ly balanced, it is proposed, by the present invention, to effect an automatic control of the balance. More specifically, since the balance depends upon proper control of the balancing currents, both with respect to the phase and magnitude, the invention involves means for indicating unbalance of phase and magnitude, together with means for independently adjusting both the phase and the magnitude ofthe balancing currents in response to any indicated unbalance.

The invention may now be more fully understood from the following description when read in connection with the accompanying drawing, the figure of which illustrates a preferred embodnnent thereof.

' Referring to the drawing, ML designates a main transmission line of a carrier system which is connected through a. hybrid coil comprising windings 10, 11 and 12 with terminal carrier apparatus TC, of any well known type, the carrier apparatus functioning to interconnect the common carrier transmission line ML with a plurality of terminal lines, such as TL TL and TL,.

The interfering wavesfrom a 'a-dio station will flow over the twosides of the main line ML in parallel, butdue. to the dissimilarity of the two sides of the lines an unbalance component will result which tends to flow serially over the two sides of the line. The unbalance component of the radio waves will produce interference in the receiving channels of the carrier apparatus TC unless suitable.measures are taken. By bridging an inductance element 13 across the conductors of the main line ML at the midpoints of the windings 10 and 11 of the hybrid coil and by taking a tap, such as 14, from the midpoint of the bridge 13, the wave component flowing over the two sides of the line in parallel (which does not cause any interference) may be received in a. suitable circuit and so translated as to neutralize the interfering component which tends to flow serially over the line.

A filter F and an artificial lineAL are included in circuit with the ground tap 14, the former being for the purpose of adjusting the phase and the latter for the purpose of adjusting the amplitude of the wave component which is to be used to balance the interfering wave component from the distant radio station. hen the amplitude and phase of the wave component have been adjusted the wave is transmitted over con,- ductors 15 to the terminal carrier apparatus TC. Itwill be observed that the interfering wave is impressed upon the carrier apparatus through the winding 12 of the hybrid coil so that if the balancing wave is of the same amplitude and is 180 out of phase with the interfering wave, the latter will be neutralized and will produce no effect upon the carrier terminal T C.

In .order to automatically maintain the proper balance of the balancing wave, a phase b-alancer PB is provided, conniprising a double vacuum tube circuit wherein the grids of both tubes are varied in potential at a phase difference of 180 by the voltage picked. up from the ground tap it after being passed through the variable filter F acting as a phase adjuster and the variable artificial line AL acting as an amplitude adjuster. The connection for this purpose is established through the input transformer 16. The interfering potentialflowing seriallyqo-ver the line wires-is im aressed upon a secondary winding 17, inductively related to thebridged inductance 18, and is applied through atrans'former 1-8 to the grids in isuch inanner as toproduce potentials upon both grids which are in phase with each other; The ,plates of both tubes are connected'to a polarized relay 19 and the operation-of thecircuit-will be'such that a phase difference of or 270 between the waves applied through transformers 10 and 1S will-cause no movement of the relay urinature- If, however, thephase difference becomes something other than 90 or 270, the relay armature will move either one contact or the other to operate a '1'110i701 controlling apparatus MP for adjusting the filter 1* until the 90 or 270 phase condition is re stored;

In order to obtain thequarter phase relation between the Waves impressed through transformers 16 and 1-8, a fixed phase shifting device20 is included in the circuit between transformers .17 and 18, this device producing a 90 phase shift in. the wave transmitted from 17 to 18. A switch 21 is also provided, and'by throwing this switch into either one of two positions the phase shift may be changed from 00 to 230 as desired.

In order to maintain the neutralizing wave of the pro-per amplitude to balance out the interfering wave, the amplitude balancer AB is provided. This consists of a double detector circuit so arranged that one side of the detector circuit is connected to the source of interfering waves through a transformer '22, while the other side of the detector circuit is connected to the balancing wave through a transformer A polar relay-2st is provided in the output circuit of the balanced detector arrangement and the rectified component from each detector tube flows through one of the windings of the polar relay. When the amplitude of the interfering wave is the same as that of the balancing wave, equal and opposite currents flow through the two windings of the polar relay 24 and its armature will remain in neutral position. If the amplitude ofone of the waves is changed with respect to that of the other, an nnba-lancing effect will be produced .so' that more current flows through one or the other of the two windings of the polar relay 2%, and its arnr ature is shifted ,in one direction or the other to operate the motor MA, which adjusts the artificial line AL until the proper balance is obtained.

Further details of the apparatus will be clear from adescription of the operation, which is as follows: Let us assume that an induced potential from av radio source is impressed upon the two line wires of the line ML and *tlowsover the two line wires in parallel, passingto ground through the two halvesof thecoil 13 and-over the conductor 14-. If the two sides' of the main line ML u ere'accurately balanced with respect to ground, no series component would result, but as this "condition is not attained in practice a series coniiponentwill flow over the upper conductor of the line ML, through the left-hand half of the winding 10, through the inductance 13, through the lefthand half of the winding 11, and back over the other side of the line .Mli. if the line ML is accurately balanced by the network N no current will flow in the network and consequently no interfering current will appear in the 'rightehand halves-of the windings 10 and 11. The interfering potential flowing over the line ML, as above described, passes through the transformer and into the terminal carrierapparatus TC.

The component of the induced wave which flows to ground over the conductor 14 does not cause any interference but passes to ground through thefirst section of the wave tilter F. A wave is accordingly propagated through the "filter F and through the artificial line AL, and thence over the conductors '15 to'the terminal carrier apparatus TC. If the wave filter F and the artilicial line ,AL are properly adjusted the an'iplitude of the wave component passing through the circuit 15 will arrive'at the terminals of. the winding 12 with the same amplitude as the interfering COTIIPOHGIH, but will be 180 out of phase-with the interfering component so that the two effects will just balance andno interference will be produced in'the te uninal apparatus TC.

Let us suppose that the filter F is not properly adjusted ,and that the interfering and balancing waves arrive at the terminals of the winding 12 in some other phase relation than 180. The balancing wave will be impressed upon the input of the phase balaucer PB through the transformer 10 and its phase relation at the transformer 10 will'be the same as its phase relation at the terminals of the winding 12. At the same time, a component corresponding to the interfering wave is impressed upon the secondary 17 and transmitted through the phase changer 20 and through the transformer 18 to the input circuit of the .phase balancer. If the balancing wave and interfering wave are in phase, and the phase shifter device 20 were not present, the component transmitted through the transformer 18 will be 180 out of phase with respect to the wave impressed upon the transformer 16. By passing through the phase shifter 20, however, its phase is displaced 90, and depending upon the setting of the switch 21., the interfering wave component transmitted from the winding 17 will shift at the transformer 18 either 90 or 270 out of phase with the component transmitted to the transformer 1.6.

The wave impressed through the transformer 16 produces opposite effects upon the grids of the two tubes, that is, effects that are 180 out. of phase with each other. The waves impressed through the transformer 18, however, produce similar effects upon both grids, that is, effects having the same phase relation. A consideration of the circuit arrangement of the phase balancer PB shows that if the wave impressed through the transformer 18 is either in phase with the wave impressed through the transformer 10 or is 180 out of phase therewith, the two waves will have additive effects upon the grid of one tube and opposing effects upon the grid of the other tube, so that the greatest possible condition of unbalance will obtain, and the armature of the polar relay 19 n'iust be shifted to one contact or the other. On the other hand, if the wave impressed through the transformer 18 is either 90 or n out of phase with the wave impressed through the transformer 16, the resultant currents flowing in the two halves of the output circuit will be equal and the armature of the relay 19 will remain in its neutral position. ment in the two waves becomes other than 90 or 270, as the case may be, the current flowing in one side of the circuit becomes greater than that flowing in the other side and the armature of the relay 19 moves to its upper or its lower position.

If the armature moves to its upper position it closes a circuit of the relay 30, whereas if it moves to its lower position it closes a circuit of relay 31. Relay 30 completes the field and armature circuits of the motor MP to drive it in one direction and relay 31 closes the circuits to drive the motor in the opposite direction. In either case, the motor will be driven in such a direction as to adjust the condensers of the filter F so that the wave impressed through the tlflllS'fOllTlGi' 16 will be brought back to quar- As soon as the displace ter phase relation with the Wave impressed through the transformer 18, whereupon the condition of balance of the circuit PB will again result and the armature of the polar relay 19 will be in neutral position.

In order to take care of the amplitude of the balancing component a wave corresponding to the interfering component is trans mitted through the winding 17, through the transformer 22 to the grid of the upper tube of the amplitude balancer AB. At the same time, a wave corresponding to the balancing component is transmitted through the transformer 23 tothe grid of the lower tube. Regardless of the phase relations of the two waves, if they are of the same amplitude they will produce direct current components in the upper and lower windings of the polar relay 24, which are equal to each other, and the armature of the relay 2st will remain in neutral position. If the amplitude of the interfering component decreases the current flow in the upper winding of the relay 2 1- deereases, the armature is shifted to its lower position, thereby closing the circuit of the relay 32 so that the motor MA is driven in such a direction as to reduce the amplitude of the balancing wave until both waves again have the same amplitude, whereupon the armature of the relay Ql will swing to its neutral position. If the amplitude of the balancing wave should be less than that of the interfering wave, a greater current; will flow through the upper winding of the relay 24 so that the armature will shift: to its upper contact and close the circuit of the relay 33, which causes the motor MA to rotate in the opposite direction, thereby adjusting the artificial line AL to increase the transmission loss of the balancing wave until its amplitude again equals that of the interfering wave, whereupon the armature of the relay 24 shifts to neutral position.

It should be noted that although the balancing wave is obtained from the same conductors of the line ML as the interfering wave, the two circuits are in effect separate and distinct circuits and a change in the attenuation of the series circuit does not necessarily produce a proportionate change in the attenuation of the circuit over the two sides of the line in parallel to ground. Likewise, the change in the propagation constant of the telephone line proper does not produce a proportionate change in the propagation constant of the circuit over the two sides of the line. Consequently, it will be apparent that a change in the phase or amplitude of the current flowing from winding 17 through the phase shifter 20 does not necessarily correspond to a similar and equal change in the phase or amplitude of the current flowing over the conductor 11.. Hence, it is necessary to automatically balance both with respect to phase and amplitude 'as above described, unless the balance adjustment is to be performed manually.

It .Willbe obvious that the general principles herein disclosed may be embodied in many other organizations widely dilifere-nt fron'i those illustrated Without departing from the spirit and scope of the invention as defined inthe appendec claims.

What is claimed is:

1 In combination with a transmission circuit subject to interfering waves an arrangement to neutralize said interfering Waves comprising means to pick up energ; from the interfering source to produce bah ancing Waves corresponding); to the 'interi en ing wave, a phase controlleraiul an amplitude controller for controlling the phase and amplitude of said balancing waives so that they may be impressed upon said transmission circuit equal vin an'iplitude and opposite in phaseto the interfering wave and means automatically ,controlhd by said interfering v-zave and said balancing wave to adji it said phase controller to maintain the waves in opposite phase relation.

:2. In combination with a transmission circuit subject to interfering Waves, an arrangen'lent to neutralize said interfering vaves comprising means to pick up energy from the interfering source to produce balancing wa -es corresponding to the interfering wave, a phase controller and an amplitude controller for controlling the pliaseand amplitude of said balancing waves so that they may be impressed upon said transnnission circuit'equal in amplitude and opposite in phase to the intertering :\vave,,and means automatitailly controlled by said interfering wave and said balancing waw to adjustsaid amplitude controller tomaintain the amplitudes of the waves the same.

3. In combination with a transmission circuit subject to interfering Waves, an arrangement to neutralize said interfering *aves (.connprising means to pick up energy from the interfering source to produce balancing waves corresponding to the interfering wave, a phase eimtroller and an amplitude controller for controlling the phase and amplitude of said balancing Waves so that they may be impressed upon said transmission circuit equal in amplitude and opposite in phase to the interleri 2' wave, means automatically controlled by said interfering Wave and said balancing wave to adjust said phase controllers to maintain the waves in opposite phase'relation, and means autoniatiailly controlled by said interfering Wave and said balancing Wave to adjust said amplitude controller to maintain the ampliti'ides ot the Waves the same.

4. In combination with a transmission circuit subject to interfering Waves an arrangement to neutralize said interfering Waves compris' igineans to pick up energy from the interfering source to produce balancing Wavescorresponding to the interfering wave; a phase controller and-an amplitude controller for controlling the phase and amplitude of said balancing-Waves so that they may be impressedu on said trans mission circuitequal inamp itude and opposite in phase to theinterfering wave and means automatically controlled by said interfering waveandlsaid balancing waves to adjust said phase controller whenever said Waves depart from their normal phase relation.

5. In combination with a transmission circuit subject to interfering Waves, an arrangement to neutralize said interfering waves comprising means to pick up ener from the interfering source to produce b ancing wavescorresponding to the ii'itertering wave, a phase controller and an amplitude controller for controlling the phase and amplitude of said balancing \WHVGS so that they may be impressed upon-said lransmission circuit equal inan'iplitude and opposite in phase to the interfering \va.ve,,and means automatically controlled by said inter'lering wave and said balancing wave for adj ustine said amplitudecontroller Whenever the amplitude ot one ofsaid Waves becomes greater than .the :other.

6. In combinationwitha transmission circuit subject to interfering wav an ar-- rangement to neutralize said interfering waves eon iprisin aneans to pick up energy l romthe interfering source to produce balancing waves corresponding to the intertering wave, a phase controller and an amplitude controller for controlling the phase and amplitude 01 said ibal-ancing waves so that they may be impressed nponsaid trammission circuit'equal in amplitude andopposite in phase to the interfering Wave, means automaticallycontrolled by said intertering wave and-said balancingwaves to adjust said phase controller wheneversaid waves depart "From their vnormal phase relation, and means antomatically controlled by said interfering wave and said balam-ingr Waves to adjust said amplitude controller whenever the amplitude oione oi? said ,waves becomes greater than the other.

7. In combinationwith a-transmission circuit subject to interfering aves. an arrangement to neutralize said interlering' waves comprising means to pick up energy from the interfering source \to produce balancing; Waves corresponding to the interfering wave, a phase controller and an amplitude controller for controlling the phase and amplitude of said balancing \va'ves so that they may be impressed upon said transmission circuit equal in amplitude and 0p positc in phase vto theinterterine' wave a phase balanc'er controlled by said interfering Wave and said balancing Wave, a relay til lUtl

normal phase relation in another direction said relay will close another contact, and means controlled over said contacts for adjusting said phase controller to bring said waves into normal phase relation.

8. In combination with a transmission circuit subject to interfering waves, an arrai'igement to neutralize said interfering waves comprising means to pick up energy 'froi'i'i the interfering source to produce balancing waves corrcspondingto the interfering wave, a phase controller and an aniplitiule controller for controlling the phase and annglitude of said balancing waves so that they may be ii'npressed upon said transmission circuit equal in an'iplitude and opposite in phase to the interfering.

wave, an amplitude balancer controlled by said interfering wave and said balancing wave, a relay associated with said amplitude balanccr, and circuits for said amplitude balancer and relay whereby when the amplitude of the balancing wave exceeds that of the interfering wave said relay will close one of its contacts, and when the amplitude of the interfering wave exceeds that of the balancing wave said relay will close another of its contacts, and means controlled over said contacts for adjusting said amplitude controller to bring both waves to the same an'iplitudc.

9. In COl'l'll')l]121tl0l1 with a transmission circuit subject to interfering Waves, an arrangen'ient to neutralize said interfering waves comprising means to pick up energy from the interfering source to produce balancing waves corresponding to the interfering wave, a phase controller and an amplitude controller for controlling the phase and amplitude of said balancing waves so that they may be impressed upon said transmission circuit equal in amplitude and opposite in phase to the interfering wave, a phase balancer controlled by said interfering wave and said balancing wave, a relay controlled by said phase lmlanccr and circuits interconnecting said relay and phase halancer so that when said waves depart from their normal phase relation in one direction said relay will close one of its contacts and when said waves depart from their normal phase relation in another direction said relay will close another contact. means controlled. over said contacts for adjusting said phase controller to bring said waves into normal phase relation, an amplitude halancer controlled by said interfering wave and said balancing wave, a relay associated with said amplitude balancer and circuits for said amplit'ude balancer and relay whereby when the amplitude of the balm-icing wave exceeds that of the interfering wave said relay will close one of its contacts and when the amplitude of the interfering wave exceeds thatof the balancing wave said relay will close another of' its contacts, and means controlled over said contacts for adjusting said a1nplitude controller to brin both waves to the same amplitude.

10. In combination with a transn'iission circuit subject to interfering waves, an arrangement to neutralize said interfering waves comprising means to pick up energy from the interfering source to produce balancing waves corresponding to the interfering wave, a phase controller and an aniplitud-e controller for controlling the phase and amplitude of said balancing waves so that they may be impressed upon said transmis sion circuit equal in amplitude and opposite in phase to the interfering wave, a phase balance-r controlled by said interfering wave and said balancing wave, said phase balancer comprising a pair of vacuum tubes, a polar relay having windings in the output circuits of said tubes, and means for impressing both said interfering wave and Said balancing wave upon the circuits of both tubes in such phase relation that when said waves are in opposite phase relation upon said main transmission circuit no effect will be produced upon said re lay but when said waves depart from their normal phase relation the efiiects upon the two tubes will be unbalanced and said relay will be actuated, and means controlled by said relay for adjusting said phase controller until said phase balancer is again balanced.

11. In combination with a transmission circuit subject to interfering waves, an arrangement to neutralize said interfering waves comprising means to pick up energy from the interfering source to produce balancing wa ves corresponding to the inter fering wave, a phase controller and an amplitude controller for controlling the phase and amplitude of said balancing waves so that they may be impressed upon said transmission circuit equal in amplitude and opposite in phase to the interfering wave, an a mplitudc balancer controlled by said interfering wave and said balancing wave, said amplitude balancer comprising a pair of vacuum tube detectors, a polar relay having windings in the output circuits of said detectors, means to impress said balancing wave upon the circuit of one of said detectors, and means to impress the interfering wave upon the circuit of the other detector so that when both waves have the same amplitude no efiect will be produced upon said polar relay and if the amplitude of one of the waves exceeds that of the other said polar relay will be actuated, and means controlled by said polar relay for adjusting: said amplitude controller to bring both wares again. to the salne'ampllt'ude;

12. In combination with a transmiSsion: circuit SUbJGClFtO1DtGIfGD1Dg:-WflVS, an arrangement) to neutralize said interfering; .W-aves. comprising means 1 to pick up energy from the interfering source to'produce bal ancing waves correspondingto the interfering Wave, a phase controller-and an ampli tude controller for cont-rollin-gthe phase and amplitude of Sttld balancingi Wavesso that they may beimpressed upon said transmission circuit equal in-amplitud'e and oppositein phase to the'int-erfering-wave, aphas-e balancer controlled by said lnterierlng Wave and said balancingv wave said phase ba-l-- tion the eliects upon the two tubes will be unbalanced and said relaywill be actuated, means controlled by said relay for adjustingisaid phase'controller until said phase baiancer is again balanced, an amplitude balaneer controlled by said interfering "uve and said balancing Wave, said amplitude balancer comprising a pair of vacuum tube detectors, a polar relay having windings in the output circuits of said detectors, means to impress said'balancing WUNG upon the circuit of one of said detectors, and means to impress the interfering wave upon the circuit of the other detector so that when both waves have the same amplitude no eliect will be produced upon saidpolar relay and it the au'iplitude of one oi? the waves exceeds that of the other said polar relay will be actuated, and means controlled by said polar relay for adjusting said amplitude controller to bring' both waresagain to the same 3111-- plitude.

In testimony whereof, I have signed my name to this'specilication this 16th day of May, 1924.

LESTER M. ILGENFRITZ. 

